Conversion of Carbon Dioxide to Methanol Using a C-H Activated Bis(imino)pyridine Molybdenum Hydroboration Catalyst

Raja Pal, Thomas L. Groy, Ryan Trovitch

Research output: Contribution to journalArticle

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Abstract

Using a multistep synthetic pathway, a bis(imino)pyridine (or pyridine diimine, PDI) molybdenum catalyst for the selective conversion of carbon dioxide into methanol has been developed. Starting from (Ph2PPrPDI)Mo(CO), I2 addition afforded [(Ph2PPrPDI)MoI(CO)][I], which features a seven-coordinate Mo(II) center. Heating this complex to 100°C under vacuum resulted in CO loss and the formation of [(Ph2PPrPDI)MoI][I]. Reduction of [(Ph2PPrPDI)MoI][I] in the presence of excess K/Hg yielded (κ6-P,N,N,N,C,P-Ph2PPrPDI)MoH following methylene group C-H activation at the α-position of one PDI imine substituent. The addition of CO2 to (κ6-P,N,N,N,C,P-Ph2PPrPDI)MoH resulted in facile insertion to generate the respective η1-formate complex, (κ6-P,N,N,N,C,P-Ph2PPrPDI)Mo(OCOH). When low pressures of CO2 were added to solutions of (κ6-P,N,N,N,C,P-Ph2PPrPDI)MoH containing pinacolborane, the selective formation of H3COBPin and O(BPin)2 was observed along with precatalyst regeneration. When HBPin was limited, H2C(OBPin)2 was observed as an intermediate and (κ6-P,N,N,N,C,P-Ph2PPrPDI)Mo(OCOH) remained present throughout CO2 reduction. The hydroboration of CO2 to H3COBPin was optimized and 97% HBPin utilization by 0.1 mol % (κ6-P,N,N,N,C,P-Ph2PPrPDI)MoH was demonstrated over 8 h at 90°C, resulting in a methoxide formation turnover frequency (TOF) of 40.4 h-1 (B-H utilization TOF = 121.2 h-1). Hydrolysis of the products and distillation at 65°C allowed for MeOH isolation. The mechanism of (κ6-P,N,N,N,C,P-Ph2PPrPDI)MoH mediated CO2 hydroboration is presented in the context of these experimental observations. Notably, (κ6-P,N,N,N,C,P-Ph2PPrPDI)MoH is the first Mo hydroboration catalyst capable of converting CO2 to MeOH, and the importance of this study as it relates to previously described catalysts is discussed.

Original languageEnglish
Pages (from-to)7506-7515
Number of pages10
JournalInorganic Chemistry
Volume54
Issue number15
DOIs
Publication statusPublished - Aug 3 2015

Fingerprint

hydroboration
Molybdenum
Carbon Monoxide
Carbon Dioxide
molybdenum
Methanol
carbon dioxide
pyridines
formic acid
methyl alcohol
catalysts
Catalysts
Imines
distillation
formates
regeneration
methylene
Distillation
imines
hydrolysis

ASJC Scopus subject areas

  • Inorganic Chemistry
  • Physical and Theoretical Chemistry

Cite this

Conversion of Carbon Dioxide to Methanol Using a C-H Activated Bis(imino)pyridine Molybdenum Hydroboration Catalyst. / Pal, Raja; Groy, Thomas L.; Trovitch, Ryan.

In: Inorganic Chemistry, Vol. 54, No. 15, 03.08.2015, p. 7506-7515.

Research output: Contribution to journalArticle

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abstract = "Using a multistep synthetic pathway, a bis(imino)pyridine (or pyridine diimine, PDI) molybdenum catalyst for the selective conversion of carbon dioxide into methanol has been developed. Starting from (Ph2PPrPDI)Mo(CO), I2 addition afforded [(Ph2PPrPDI)MoI(CO)][I], which features a seven-coordinate Mo(II) center. Heating this complex to 100°C under vacuum resulted in CO loss and the formation of [(Ph2PPrPDI)MoI][I]. Reduction of [(Ph2PPrPDI)MoI][I] in the presence of excess K/Hg yielded (κ6-P,N,N,N,C,P-Ph2PPrPDI)MoH following methylene group C-H activation at the α-position of one PDI imine substituent. The addition of CO2 to (κ6-P,N,N,N,C,P-Ph2PPrPDI)MoH resulted in facile insertion to generate the respective η1-formate complex, (κ6-P,N,N,N,C,P-Ph2PPrPDI)Mo(OCOH). When low pressures of CO2 were added to solutions of (κ6-P,N,N,N,C,P-Ph2PPrPDI)MoH containing pinacolborane, the selective formation of H3COBPin and O(BPin)2 was observed along with precatalyst regeneration. When HBPin was limited, H2C(OBPin)2 was observed as an intermediate and (κ6-P,N,N,N,C,P-Ph2PPrPDI)Mo(OCOH) remained present throughout CO2 reduction. The hydroboration of CO2 to H3COBPin was optimized and 97{\%} HBPin utilization by 0.1 mol {\%} (κ6-P,N,N,N,C,P-Ph2PPrPDI)MoH was demonstrated over 8 h at 90°C, resulting in a methoxide formation turnover frequency (TOF) of 40.4 h-1 (B-H utilization TOF = 121.2 h-1). Hydrolysis of the products and distillation at 65°C allowed for MeOH isolation. The mechanism of (κ6-P,N,N,N,C,P-Ph2PPrPDI)MoH mediated CO2 hydroboration is presented in the context of these experimental observations. Notably, (κ6-P,N,N,N,C,P-Ph2PPrPDI)MoH is the first Mo hydroboration catalyst capable of converting CO2 to MeOH, and the importance of this study as it relates to previously described catalysts is discussed.",
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N2 - Using a multistep synthetic pathway, a bis(imino)pyridine (or pyridine diimine, PDI) molybdenum catalyst for the selective conversion of carbon dioxide into methanol has been developed. Starting from (Ph2PPrPDI)Mo(CO), I2 addition afforded [(Ph2PPrPDI)MoI(CO)][I], which features a seven-coordinate Mo(II) center. Heating this complex to 100°C under vacuum resulted in CO loss and the formation of [(Ph2PPrPDI)MoI][I]. Reduction of [(Ph2PPrPDI)MoI][I] in the presence of excess K/Hg yielded (κ6-P,N,N,N,C,P-Ph2PPrPDI)MoH following methylene group C-H activation at the α-position of one PDI imine substituent. The addition of CO2 to (κ6-P,N,N,N,C,P-Ph2PPrPDI)MoH resulted in facile insertion to generate the respective η1-formate complex, (κ6-P,N,N,N,C,P-Ph2PPrPDI)Mo(OCOH). When low pressures of CO2 were added to solutions of (κ6-P,N,N,N,C,P-Ph2PPrPDI)MoH containing pinacolborane, the selective formation of H3COBPin and O(BPin)2 was observed along with precatalyst regeneration. When HBPin was limited, H2C(OBPin)2 was observed as an intermediate and (κ6-P,N,N,N,C,P-Ph2PPrPDI)Mo(OCOH) remained present throughout CO2 reduction. The hydroboration of CO2 to H3COBPin was optimized and 97% HBPin utilization by 0.1 mol % (κ6-P,N,N,N,C,P-Ph2PPrPDI)MoH was demonstrated over 8 h at 90°C, resulting in a methoxide formation turnover frequency (TOF) of 40.4 h-1 (B-H utilization TOF = 121.2 h-1). Hydrolysis of the products and distillation at 65°C allowed for MeOH isolation. The mechanism of (κ6-P,N,N,N,C,P-Ph2PPrPDI)MoH mediated CO2 hydroboration is presented in the context of these experimental observations. Notably, (κ6-P,N,N,N,C,P-Ph2PPrPDI)MoH is the first Mo hydroboration catalyst capable of converting CO2 to MeOH, and the importance of this study as it relates to previously described catalysts is discussed.

AB - Using a multistep synthetic pathway, a bis(imino)pyridine (or pyridine diimine, PDI) molybdenum catalyst for the selective conversion of carbon dioxide into methanol has been developed. Starting from (Ph2PPrPDI)Mo(CO), I2 addition afforded [(Ph2PPrPDI)MoI(CO)][I], which features a seven-coordinate Mo(II) center. Heating this complex to 100°C under vacuum resulted in CO loss and the formation of [(Ph2PPrPDI)MoI][I]. Reduction of [(Ph2PPrPDI)MoI][I] in the presence of excess K/Hg yielded (κ6-P,N,N,N,C,P-Ph2PPrPDI)MoH following methylene group C-H activation at the α-position of one PDI imine substituent. The addition of CO2 to (κ6-P,N,N,N,C,P-Ph2PPrPDI)MoH resulted in facile insertion to generate the respective η1-formate complex, (κ6-P,N,N,N,C,P-Ph2PPrPDI)Mo(OCOH). When low pressures of CO2 were added to solutions of (κ6-P,N,N,N,C,P-Ph2PPrPDI)MoH containing pinacolborane, the selective formation of H3COBPin and O(BPin)2 was observed along with precatalyst regeneration. When HBPin was limited, H2C(OBPin)2 was observed as an intermediate and (κ6-P,N,N,N,C,P-Ph2PPrPDI)Mo(OCOH) remained present throughout CO2 reduction. The hydroboration of CO2 to H3COBPin was optimized and 97% HBPin utilization by 0.1 mol % (κ6-P,N,N,N,C,P-Ph2PPrPDI)MoH was demonstrated over 8 h at 90°C, resulting in a methoxide formation turnover frequency (TOF) of 40.4 h-1 (B-H utilization TOF = 121.2 h-1). Hydrolysis of the products and distillation at 65°C allowed for MeOH isolation. The mechanism of (κ6-P,N,N,N,C,P-Ph2PPrPDI)MoH mediated CO2 hydroboration is presented in the context of these experimental observations. Notably, (κ6-P,N,N,N,C,P-Ph2PPrPDI)MoH is the first Mo hydroboration catalyst capable of converting CO2 to MeOH, and the importance of this study as it relates to previously described catalysts is discussed.

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